The present invention relates to a support structure for an airbag apparatus that allows an airbag apparatus to be supported by the steering wheel in a vehicle such as an automobile.
For example, Japanese Laid-Open Patent Publication No. 2016-30552 discloses a structure in which, as shown in FIG. 17, an airbag apparatus 50 is used as the damper mass of a dynamic damper, and the airbag apparatus 50 is supported by a steering wheel 52. This support structure includes a pin 53, a pin holder 54, a damper holder 55, and an elastic member 56.
The pin 53 has a shaft portion 53a extending in the front-rear direction. The shaft portion 53a is passed through a mounting hole 51a of a bag holder 51 of the airbag apparatus 50. The shaft portion 53a has at the rear end a flange portion 53b having an outer diameter greater than the inner diameter of the mounting hole 51a. The pin 53 is attached to the steering wheel 52 by a snap-fit structure at the front end of the shaft portion 53a and supports the airbag apparatus 50 at the rear of the shaft portion 53a. The pin holder 54 slidably covers the shaft portion 53a in a state of being passed through the mounting hole 51a and is urged rearward by an urging member 57. The damper holder 55 includes an annular plate-shaped bottom wall portion 55a and a cylindrical circumferential wall portion 55b extending rearward from the outer circumferential portion of the bottom wall portion 55a. The damper holder 55 is mounted to the airbag apparatus 50 while covering part of the pin holder 54. The elastic member 56 includes an elastic body portion 56a and an annular protrusion 56b. The elastic body portion 56a is annular and is arranged between the pin holder 54 and the damper holder 55. The annular protrusion 56b is provided on the outer circumferential portion of the rear end of the elastic body portion 56a. The annular protrusion 56b is in contact with the rear end face of the circumferential wall portion 55b of the damper holder 55.
A motion transmitting portion 55c is provided on the inner circumferential portion of the bottom wall portion 55a. The motion transmitting portion 55c extends forward and is passed through the mounting hole 51a. A motion receiving portion 54a protrudes from part of the outer circumferential surface of the pin holder 54 that is immediately forward of the motion transmitting portion 55c. The motion transmitting portion 55c and the motion receiving portion 54a are configured to transmit forward motion of the damper holder 55 to the pin holder 54.
A gap G1 exists inside the motion transmitting portion 55c. A tubular noise suppressing portion 56c, which is made of a material softer than the pin holder 54, is provided inside the gap G1. The noise suppressing portion 56c extends forward from the inner circumferential portion of the elastic body portion 56a and constitutes part of the elastic member 56.
In the above described support structure, the airbag apparatus 50 functions as the damper mass of a dynamic damper, and the elastic body portion 56a functions as the spring of the dynamic damper. That is, when the steering wheel 52 vibrates, the elastic body portion 56a vibrates together with the airbag apparatus 50 while being elastically deformed at a resonance frequency that is the same as or close to the frequency of the vibration, so that the elastic body portion 56a absorbs the vibration energy of the steering wheel 52. Due to such energy absorption, the vibration of the steering wheel 52 is suppressed.
When the airbag is inflated rearward at the activation of the airbag apparatus 50, rearward force is applied to the bag holder 51. The flange portion 53b of the pin 53 functions as a stopper by being positioned behind the peripheral portion of the mounting hole 51a of the bag holder 51, which moves rearward. The flange portion 53b restrains the bag holder 51 and thus the airbag apparatus 50 from coming off the pin 53.
Furthermore, when the vibration of the steering wheel 52 is transmitted to the airbag apparatus 50, the noise suppressing portion 56c restrains the hard motion transmitting portion 55c and the hard pin holder 54 from directly contacting each other, thereby preventing generation of noise due to contact between the motion transmitting portion 55c and the pin holder 54.
In order to prevent the bag holder 51 from coming off the pin 53 as described above, the difference between the inner diameter of the mounting hole 51a and the outer diameter of the flange portion 53b is preferably increased by reducing the inner diameter of the mounting hole 51a. This is because such reduction in the inner diameter of the mounting hole 51a will increase the region in the flange portion 53b that restricts the rearward motion of the bag holder 51.
In addition to the shaft portion 53a of the pin 53, Japanese Laid-Open Patent Publication No. 2016-30552 passes, through the mounting hole 51a, the pin holder 54, the motion transmitting portion 55c of the damper holder 55, the gap G1, and the noise suppressing portion 56c of the elastic member 56. Therefore, the inner diameter of the mounting hole 51a is affected by the shaft portion 53a, the pin holder 54, the motion transmitting portion 55c, the gap G1, and the noise suppressing portion 56c. 
In this regard, the noise suppressing portion 56c of Japanese Laid-Open Patent Publication No. 2016-30552 simply extends forward from the inner circumferential portion of the elastic body portion 56a, which functions as the spring of the dynamic damper. The noise suppressing portion 56c is thus one factor that independently increases the inner diameter of the mounting hole 51a. Therefore, there is still room for improvement in preventing the bag holder 51 from coming off the pin 53 by reducing the inner diameter of the mounting hole 51a. 